In electrooptical display elements containing liquid crystal dielectrics, the electrooptical effect of the display can be produced by embedding pleochroic dyestuffs ("guest phase") in a liquid crystal matrix ("host phase"). In this context, see the surveys by COX, Mol. Cryst. Liq. Cryst., Volume 55, pages 1-32 (1979); JONES and REEVE, ibid., Volume 60, pages 99-110 (1980); GRAY, Chimia, Volume 34, pages 47-58 (1980) and the literature quoted therein, all of whose disclosures are entirely incorporated by reference herein.
However, the dyestuffs which have hitherto been used for this purpose, in particular the red dyestuffs hitherto used, fulfill the imposed requirements (for example high order parameter, satisfactory solubility in the host phase, and stability to UV and visible light and to voltages of up to about 20 V) only to an unsatisfactory extent.